Conventionally, there is known a gas discharge tube including a sealed container in which a gas (deuterium gas) is sealed, an anode disposed within this sealed container, a cathode which is spaced from the anode in the sealed container and generates discharge between the cathode and the anode, and a conductive part restricting a discharge path which is disposed between the anode and the cathode to narrow the discharge path. In such a type of gas discharge tube, as described in Patent document 1 and 2 listed below, the cathode is formed by applying thermionic emission material onto a coil (filament coil) that functions as a heater. In the technique of the Patent document 1, the cathode is enclosed by a metal-made electrode enclosure having an opening for electron emission, and in the Patent document 2, it is enclosed by a metal-made front cover and a discharge rectifier plate having an electron discharge window.
Patent document 1: Japanese Unexamined Patent Publication No. H07-288106
Patent document 2: Japanese Unexamined Patent Publication No. 2002-151008